Such tracklaying gears are used for various machines of the type mentioned above such as hydraulic or cable excavators, mobile crawler cranes, bulldozers, asphalt milling machines or Surface Miners. The endlessly circulating track chain traditionally is a link chain made of a metallic material, but it can also mean a rubber chain or a similarly constructed moving belt which circulates endlessly.
To protect the crawler drive against external damages and not increase the track width of the vehicle beyond the outer sides of the link chains, the crawler drive for driving the link chain is integrated into the tracklaying gear, in particular such that the crawler drive is arranged within the path of circulation of the track chain, so that no or at least no significant protrusion does exist. However, this results in various problems.
On the one hand, the drive unit must have a very short overall length, so as not to laterally protrude beyond the track chain. The available installation space substantially is defined by the width of the track chain, so that longer motors with transmission units connected thereto often are too long or could only be mounted with a lateral protrusion.
On the other hand, cooling the drive units often is not possible to a sufficient extent, since a surface cooling or open-circuit cooling is not expedient for reasons of dust input. In addition, the crawler drive in use can also partly be submerged in water, so that a closed design of the drive units must be provided. In the case of forced ventilations, in addition, a strong generation and agitation of dust can be caused by a large stream of air emerging from the drive unit depending on the soil at the site of use, which is not acceptable in most uses.
Due to their short overall length and easy coolability, hydrostatic motors therefore are often used as crawler drive, which drive the tumbler of the tracklaying gear via a planetary transmission and are provided with a hydraulically ventilated multi-disc brake. Due to the small overall length of such hydrostatic motors, it mostly is possible to keep the axial overall length of motor and transmission so short that the entire drive unit can completely be accommodated in the region of the chain width and thus can be well protected against external influences and damages for example by stones.
In addition it has already been considered to use electric motors instead of such hydrostatic drives as crawler drive. However, this is not easily possible for the above-mentioned reasons and problems.
Usually, electric motors are cooled by surface cooling or open-circuit cooling with forced ventilation or self-ventilation. These known cooling solutions are, however, not expedient for use in tracklaying gears of construction machines, surface milling cutters, asphalt milling machines, excavators or the like for reasons of dust input which can be produced by a tracklaying gear operating in or on the soil. In addition, in use the drive might also partly be submerged in water, so that a closed design of the motor is preferred. On the other hand, a strong generation and agitation of dust can be caused by a large stream of air emerging from the motor depending on the soil at the site of use, which is not acceptable in most uses.
In so far, it has already been considered to provide for sucking in cooling air via a kind of snorkel at a higher point of the machine, since less dust is generated there and hence a reduced dust input into the motor is achieved. However, this does not solve the problem of the generation of dust by the emerging cooling air.
The generation of dust can largely be avoided with a hermetically closed motor in which the emerging cooling air is contained in a conduit and recirculated to an outlet at an elevated point on top of the machine. Nevertheless, a rest of dust input into the motor will remain, since the intake conduit cannot be designed arbitrarily high.
Therefore, it has already been considered to employ a hermetically closed motor, in which the air is guided in a closed air circuit and is cooled by means of a heat exchanger with an air inlet and outlet located at the top. However, this involves the problem that the required large amounts of air require very large conduit cross-sections down into the tracklaying gear and back, which in terms of space can hardly be accommodated and can only be protected against mechanical damages with corresponding difficulties.